1. Field of Invention
The present invention relates to a method for signal processing, and, more particularly, to a method for the processing of multiple signals of different frequencies which provides a reduction in processing required for the extraction of information from those signals.
2. Description of Prior Art
The digital sampling of signals is well understood throughout industry and academia. The analog to digital sampling rate is typically performed at or above the Nyquist frequency, which refers to the minimum rate at which a signal must be measured in order to extract all available information from the given signal. In general, the Nyquist frequency is a frequency that is equivalent to the frequency of the maximum bandwidth of the signal under analysis. In the case that multiple signals are being simultaneously measured, the Nyquist frequency is equivalent to the difference between the highest and lowest absolute frequency of the signals under analysis. Examples of applications for which the simultaneous processing of multiple frequencies may be utilized include radar (particularly MIMO, and/or multistatic), communications, electronic warfare, and general purpose receivers for arbitrary functions.
Multiple-input multiple-output (“MIMO”) uses multiple transmitting and receiving antennas to improve the capabilities of a variety of systems including communications and radar. With multiple transmitting antennas, a MIMO system is capable of simultaneously sending more than one data stream or signal. Similarly, the receiver antennas of a MIMO system can receive multiple data streams or signals. The ability to receive multiple signals allows a MIMO system to surmount problems associated with multipath effects in which transmitted information is scattered by obstacles and reaches the receiving antennas at different times with different angles.
MIMO systems often utilize multiple transmit waveforms in which the waveforms of the many multiplexed signals transmitted simultaneously by the transmit antennas are varied to make them separable. In other words, each transmit antenna transmits a waveform that is separable from the signals transmitted by the other transmit antennas. Thus, while each receive antenna will simultaneously receive all the transmitted waveforms, each individual waveform must be separable from the other signals. Individual waveforms can be made separable through phase/amplitude coding, amplitude (time), frequency, or other methods.
Frequency orthogonal MIMO systems utilize frequency multiplexing in which a diverse frequency is transmitted by each transmit antenna. Upon receive, the processing of multiple waveforms of different frequency typically require a very large amount of processing power to separate when received, due to the Nyquist frequency sampling required and the subsequent processing to separate the frequencies. As such, there is still a need for a mechanism that further reduces the processing power required by a frequency-orthogonal MIMO system.
Similarly, multi-static radar systems rely on energy transmitted from one or more sources cooperatively or non-cooperatively. These signals are often different frequencies to enable separability.
Similarly, receivers for the purpose of electronic intelligence or electronic warfare are typically required to receive a broad range of signals that are separated in frequency.
Similarly, receivers for general purposes will typically be required to receive a broad range of signals at different frequencies.